The invention relates to a steering device, especially for agricultural tractors and similar commercial vehicles having a rigid steering axle movable in a pendulum fashion around a pendulum pin, the pendulum pin being arranged in line with the longitudinal central axis of the tractor, the wheels of which are driven by a cardan shaft arranged between the steering axle and the transmission the transmission being located with distance behind the steering axle, comprising a power steering gear having a pinion, which is connected with the steering linkage of the steering axle, and comprising a steering cylinder being an integral part of the steering linkage, the steering cylinder being actuatable by fluid under pressure supplied by the power steering gear.
Commercial vehicles having a construction to allow a maximum speed of more than 62 km/h have to have steering devices including a mechanical connection throughout from the steering wheel to the directed wheels. Such a steering device known from DE-AS 12 88 930 is hydraulically power assisted but can be controlled in emergency steering using increased steering forces when the power steering fails.
Farming tractors having a construction for a maximum speed below the limit described above at present are designed including pure hydraulic steering devices. The reason for this was the fact that there was not enough room to arrange a mechanical steering device as used before extending from the steering wheel to the steering axle being positioned far in front of the steering wheel. The only solution was to use the room beside the driving engine above the steering axle. However, this arrangement greatly limits the possible angle of the steering action. Hydraulic steering devices include a power steering gear operated by the steering wheel supplying hydraulic liquid under pressure to the power steering cylinder. The power steering cylinder, as known from DE-AS 1 21 724, is arranged parallel to the body of the steering axle and connected with the steering linkage of the steering axle. This arrangement, particularly in view of the large dimensions of the steering cylinder, require substantial room for its positioning. This hinders the construction as far as the room is needed to position other essential elements of the tractor such as the front power take-off shaft, power lift elements, axle suspension elements for example.
It is the object of the invention to provide a steering device being adapted to farming tractors and other commercial vehicles having a construction to allow a maximum speed of more than 50 km/h.
This is attained by the features of patent claim 1.
Using a steering cylinder having two chambers with the same cross section and positioning it in a region between the steering axle and the transmission gives the possibility to use the space already housing the cardan shaft for driving the front wheels. Thus, this room is used for two purposes. Furthermore, the invention allows the piston rod to serve two purposes. First, the piston rod serves to transmit the power force generated by the hydraulic fluid acting on the piston to the steering linkage of the steering axle. Second, there always is a mechanical connection from the power steering gear to the steering linkage. Futhermore, there is more room to be used to position other essential elements as the front power take-off shaft, power lift elements, axle suspension elements in the region of the steering axle and, sensitive parts of the steering cylinder as the piston rod and the conduits are positioned in the interior and thus protected against damage.
Design of the region around the steering wheel in the cabin is simpler and more economical, since the power steering gear no longer needs to be positioned in this region.
The features of claim 3 facilitate use of the invention on vehicles having a suspended steering axle.
The subject of claims 4 to 8 is a useful arrangement of the power steering cylinder being part of the steering linkage of the steering axle.
The features of claim 9 can be used on vehicles including a cardan shaft for driving the front wheels. The cardan shaft being positioned in the interior of piston rod is protected from damage and dirt.
A very simple design of the steering device is subject of claim 10.
The power steering gear according the features of claim 11 allows the steering device to have substantially shortened conduits.